Left anterior hemiblock

This ECG is taken from an 82-year-old man who called 911 because of chest pain. He has an unspecified “cardiac” history, but we do not know the specifics.

WHAT IS THE RHYTHM? The heart rate is 69 bpm, and there are P waves before every QRS complex. The underlying rhythm is regular, with one premature beat that is wide without a P wave. The PR interval is slightly prolonged at .25 seconds. The rhythm is normal sinus rhythm with first-degree AV block and one PVC.

WHY THE WIDE QRS? The QRS complex is wide at .14 seconds. The QRS in V 1 has a wide R wave after a small Q wave. This in consistent with right bundle branch block pattern, with loss of the normal initial small r wave (pathological Q waves). The diagnosis of RBBB is further corroborated by the wide little S waves in Leads I and V6. The QRS frontal plane axis is -66 degrees per the machine, and clearly “abnormal left” because the QRS in Lead II is negative, while the QRS in Leads I and aVL are positive. This is left anterior fascicular block, also called left anterior hemiblock. The combination of RBBB and LAFB is a common one, as the two branches have the same blood supply. It is also called bi-fascicular block.

WHAT ABOUT THE ST SEGMENTS? The ST segments in leads V2 through V6 are elevated, and their shape is very straight, as opposed to the normal shape of coved upward (smile). Even though the amount of ST elevation at the J points appears subtle, the shape of the segments, the fact that they appear in related leads, and the fact that the patient is an elderly male with chest pain all point to the diagnosis of ANTERIOR WALL ST elevation M.I. (STEMI). Additional ST changes include a straight shape in Leads I and aVL and ST depression in V1 and aVR.

PATIENT OUTCOME The patient was transported to a cardiac center, where he received angioplasty in the cath lab. The left coronary artery was found to be occluded, and was repaired and stented. He recovered without complications and was sent home in a few days.

Today’s ECG is from a 75 year old man who has been experiencing syncope.

Examination of the ECG shows a sinus bradycardia at just under 40 bpm. There is a first-degree AV block, with a PR interval of about .28 seconds (280 ms). There is a right bundle branch block. The ECG criteria for right bundle branch block are: supraventricular rhythm, wide QRS (120 ms in this case), rSR’ pattern in V1, and a small, wide S wave in Leads I and V6. There is actually a “terminal delay”, or extra wave at the end of each QRS complex, reflecting late repolarization of the right ventricle.

This ECG also shows a left anterior fascicular block, also called left anterior hemiblock. The left bundle branch usually has two main branches, the anterior-superior and the posterior-inferior. ECG criteria for left anterior fascicular block are: left axis deviation with a small r wave in Lead III and a small q waves with tall R waves in Leads I and aVL. There is also a prolonged R wave peak time (> 45 ms) in aVL. There is usually a slightly prolonged QRS, but in this case, there is widening of the QRS due to the RBBB. Because the right bundle branch is blocked, and one fascicle of the left bundle is blocked, the patient is said to have a “bifascicular block”. Only one fascicle remains available for conduction from the atria to the ventricles.

We have no information about what caused the conduction block in these two fascicles, but should the third fascicle fail, the patient will be in a complete AV block. An AV block at the level of the bundle branches will result in an idioventricular escape rhythm – wide QRS complexes with very slow rates – which is a low-output rhythm.

This patient has also had syncope, which was determined to be related to his bradycardia. He had an AV sequential pacemaker implanted and did well.

This series of three ECGs is from a 60-year-old man who was brought to the Emergency Department after being involved in a motor vehicle accident. No injuries were found, but the patient was severely intoxicated by alcohol consumption. He was conscious but agitated.

ECG NO. 1 15:07:23

The first ECG was taken by fire-rescue personnel at the scene of the accident. His hemodynamic status was stable, and the rate was not addressed in the field. ECG No. 1 shows a supraventricular rhythm at 161 bpm, with a narrow QRS and P waves visible before each QRS.

A notable feature of this ECG are the left axis deviation, by default diagnosed at left anterior hemiblock (left anterior fascicular block). The .10 second QRS width is typical of LAHB, as is the rS pattern in Lead III.

Also noted is the unusual R wave progression in the precordial leads. The R waves are prominent in V2, and then fail to progress across the precordium, and the S waves persist. This is probably due to the hemiblock.We do not know this patient’s medical history, except that he self-described as an “alcoholic”.LAFB can be associated with coronary artery disease.

ECG NO. 2 15:20:38

Now being evaluated in the Emergency Dept., we see the patient's heart rate is 163 bpm. Some variability in the rate was noted with patient agitation and activity, so it was determined that the rhythm was probably sinus tachycardia. There were no other significant changes in the ECG from the first one. Unfortunately, we no longer have access to lab results, so we do not know his electrolyte or hydration status. Labs confirmed ETOH intoxication.

We have no clinical information about this patient, except that he was complaining of chest pain, and was initially treated by prehospital paramedics.

ST Changes The paramedics noted a slight J point elevation in the precordial leads, specifically about one mm of elevation in Leads V2, V3, and V4. In addition, the ST segments are curved downward like a frown in V1 and straight in the remaining precordial leads. Because of the patient’s symptoms, and the ST abnormalities, they notified the hospital that they believed this was a STEMI. The patient was transported without complications, and the Emergency Department physician subsequently downgraded the initial assessment of STEMI Alert. We do not have access to follow up. These ST segments are abnormal, but do not necessarily indicate an acute ST-elevation M.I. (STEMI). A flat or “frowning” ST segment DOES suggest coronary artery disease, and the patient’s symptoms are worrisome.However, before activating the cath lab emergently, it is sometimes preferable to observe the patient, check cardiac enzymes and other lab results, and repeat ECGs.

Are These ST Changes Due to Acute M.I.? There are several accepted guidelines in use for evaluating ST segments for STEMI. Some are simplified for ease of use, and some are very detailed, taking into consideration the patient’s age and gender. There are ECG features that INCREASE the chances of ST elevation being due to acute M.I. These features include:

This ECG provides an example of LEFT ANTERIOR FASCICULAR BLOCK (LAFB). It is from a 71-year-old woman for whom we have no other history. She also has first-degree AV block and right bundle branch block. RBBB and LAFB together are called bifascicular block. It is not uncommon to see this type of bifascicular block, as the right bundle branch and the anterior fascicle of the left bundle share a blood supply.

The conduction system below the AV node consists of the Bundle of His, the left bundle branch, and the right bundle branch. While there is some variation among individuals, most of us have two main fascicles, or branches, of the left bundle. The ANTERIOR-SUPERIOR fascicle carries the electrical impulse to the anterior wall of the left ventricle, and the POSTERIOR - INFERIOR fascicle carries the impulse to the inferior area of the left ventricle.

Blocks can occur at any level in the conduction system, including left bundle branch block, right bundle branch block, left anterior fascicular block, left posterior block, and bi-fascicular blocks. LAFB can have many causes, including myocardial infarction, cardiomyopathies, fibrosis of the cartilagenous ring, and aortic valve disease. Left anterior fascicular block is much more common than left posterior fascicular block. Both are also called hemiblocks.

When LAFB is present, the initial septal depolarization forces are still left to right, providing a small initial q wave in Lead I and a small r wave in Lead III. After septal depolarization is complete, the activation vector moves inferiorly and to the right as the electrical wavefront moves through the left posterior hemifascicle and right bundle branch. The impulse finally makes its way to the left and superiorly via slow conduction through myocardium normally depolarized by the left anterior hemifascicle, which is blocked. It is because the terminal left ventricular activation moves upward and toward the left that the inferior leads have negative deflections.

This ECG provides an example of LEFT ANTERIOR FASCICULAR BLOCK (LAFB). It is from an elderly woman for whom we have no other history.

The conduction system below the AV node consists of the Bundle of His, the left bundle branch, and the right bundle branch. While there is some variation among individuals, most of us have two main fascicles, or branches, of the left bundle. The ANTERIOR-SUPERIOR fascicle carries the electrical impulse to the anterior wall of the left ventricle, and the POSTERIOR - INFERIOR fascicle carries the impulse to the inferior area of the left ventricle.

Blocks can occur at any level in the conduction system, including left bundle branch block, right bundle branch block, left anterior fascicular block, left posterior block, and bi-fascicular blocks. LAFB can have many causes, including myocardial infarction, cardiomyopathies, fibrosis of the cartilagenous ring, and aortic valve disease. Left anterior fascicular block is much more common than left posterior fascicular block. Both are also called hemiblocks.

When LAFB is present, the initial septal depolarization forces are still left to right, providing a small initial q wave in Lead I and a small r wave in Lead III. After septal depolarization is complete, the activation vector moves inferiorly and to the right as the electrical wavefront moves through the left posterior hemifascicle and right bundle branch. The impulse finally makes its way to the left and superiorly via slow conduction through myocardium normally depolarized by the left anterior hemifascicle, which is blocked. It is because the terminal left ventricular activation moves upward and toward the left that the inferior leads have negative deflections.

The diagnostic criteria for LAFB are: LEFT AXIS DEVIATION (QRS axis between -45 degrees and -90 degrees); qR pattern in Lead I; rS pattern in Lead III; delayed activation time evident in Lead aVL - the time from onset of the QRS to the peak of the R wave is 45 ms or more. (This example barely makes that criteria); QRS duration normal or slightly wide, but not 120 ms or more (unless there is also RBBB). LAFB also causes poor R wave progression in the precordial leads, with late transition and S wave present in V6.

Before deciding on a diagnosis of LAFB, you must rule out previous or acute INFERIOR WALL M.I. The pathological Q waves that can occur with necrosis can cause a left axis deviation in the frontal plane. The presence of a small r wave in Lead III rules out pathological Q wave in that lead. If any fascicular block (hemiblock or bundle branch block) occurs during the course of an M.I., the patient should be watched carefully for progression of the block. Be prepared to pace if necessary in that situation.

This is a nice, clear right bundle branch block pattern: wide QRS, supraventricular rhythm (NSR), and rSR' pattern in V1. Wide little s waves in Leads I and V6 are also diagnostic. The left axis deviation indicates a left anterior fascicular block, since there is no other apparent reason for the left axis deviation, such as pathological Q waves or LVH. Left anterior fascicular block is a diagnosis of exclusion, also considering that RBBB and LAFB are often seen together (bifascicular block), since the two fascicles have the same blood supply.

A good example of aberrantly conducted premature beats (PACs or possibly PJCs) that are conducted with a left anterior fascicular block. The underlying rhythm is sinus at about 80/min. The timing of the premature beats is best seen in the Lead II rhythm strip at the bottom, as this ECG machine does not print the 12 leads in an uninterrupted manner. You will see interruptions each time the leads change.

The first beat on the ECG is one of the premature beats. You can observe the left axis deviation without pathological Q waves. Lead I shows the premature beats with an Rs pattern, and Leads II and III have rS. The early beats have caught the anterior fascicle of the left bundle branch refractory from the preceding beat. It recovers for the normally-timed sinus beats.

From June 10, 2012: As is the case with all practical blogs, I’m encouraging ECG Guru members to engage in active group participation. Share your thoughts, observations, impressions, findings, and interpretations. Feel free to compare notes with one another and pick each other’s brains.